A typical circuit board assembly includes a section of circuit board material (e.g., layers of FR4, copper, plated-through holes, etc.), circuit board components (e.g., integrated circuit devices, discrete capacitors, resistors and diodes, connectors, etc.), and supplemental hardware (e.g., heat sinks, insertion/extraction levers, etc.). The section of circuit board material includes layers of conductive and non-conductive material sandwiched together to form a network of electrical pathways that connect the circuit board components together.
FIG. 1 shows a schematic diagram for a circuit 20 which utilizes differential-mode communications through one or more circuit boards. The circuit 20 includes two circuit board components 22(A), 22(B) (collectively, circuit board components 22) which are configured to communicate with each other through a differential link 24 having a first pair of differential signal pathways 26(AB) (or simply a differential pair 26(AB)) leading from the component 22(A) to the component 22(B), and a second differential pair 26(BA) leading from the component 22(B) to the component 22(A).
Each component 22 includes a transmitter 28 and a receiver 30. In particular, the component 22(A) includes a transmitter 28(A) which is configured to transmit a differential signal 32(AB) to a receiver 30(B) of the component 22(B) through the differential pair 26(AB). Similarly, the component 22(B) includes a transmitter 28(B) which is configured to transmit a differential signal 32(BA) to a receiver 30(A) of the component 22(A) through the differential pair 26(BA).
More specifically, each transmitter 28 (e.g., see the transmitter 28(B)) includes a serial input 34, a differential signal output 36 (i.e., a positive output 36(+) and a negative output 36(−)), a core voltage terminal 38, an input/output (I/O) voltage terminal 40, and a ground terminal 42. Similarly, each receiver 30 (e.g., see the receiver 30(A)) includes a differential signal input 44 (i.e., a positive input 44(+) and a negative input 44(−)), a serial output 46, a core voltage terminal 48, an input/output (I/O) voltage terminal 50, and a ground terminal 52. The ground terminal 42 of each transmitter 28 and the ground terminal 52 of each receiver 30 connect to a common ground 54 through a contiguous conductor 56 (e.g., a common ground plane in the context of a single circuit board). It should be understood that, although the ground terminals 42, 52 of the transmitter 28(B) and the receiver 30(A) are not shown connected to the common ground 54 for simplification of FIG. 1, these ground terminals 42, 52 do connect to the common ground 54 through the contiguous conductor 56.
Furthermore, each differential pair 26(AB), 26(BA) (e.g., see the differential pair 26(AB)) includes a positive line 58(+) configured to carry a positive signal relative to the common ground 54, a negative line 58(−) negative signal relative to the common ground 54, and a direct current (DC) blocking capacitor 60 in the middle of each line 58(+), 58(−). The DC blocking capacitors 60 block the passage of direct current through the positive and negative lines 58(+), 58(−) (i.e., to provide DC electrical separation) and thus enable the components 22 at the ends of the differential pairs 26(AB), 26(BA) to connect to different voltages, as well as enjoy I/O protection during hot insertion (in the context of multiple circuit boards) and power up.